To operate a heat source machine, for example, a chiller on the design values, it is necessary to manage a flow rate of a heat transfer medium (chilled water) flowing into an evaporator, but a flow meter for measuring the flow rate of the heat transfer medium may not be provided in the chiller because a flow meter for measuring a flow rate is expensive, and it is required to reduce the number of components and so on.
Therefore, as the technologies for measuring a flow rate, PTL 1 discloses the estimation system of cooling water flow rate in that a chilling load is computed based on measurement values of an outlet temperature of chilled water, an inlet temperature of the chilled water and a flow rate of the chilled water, a heat exchange coefficient is computed based on the inlet temperature of the chilled water and the chilling load, and a flow rate of a cooling water is derived from measurement values sent from a group of sensors and the heat exchange coefficient, and then output it.
PTL 2 describes the technology in that for a plurality of air conditioning machines, a plurality of differential pressure sensors are provided to measure a differential pressure between an inlet and an outlet of chilled and heated water in each of the plurality of air conditioning machines and a flow sensor is provided to measure the entire flow rate of the chilled and heated water, and by providing a flow path allowing only one differential pressure sensor to operate through valve switching and the like, the relation between the flow rate and the differential pressure is obtained before operation of cooling, and on the operation of cooling, a flow rate of the chilled and heated water is obtained using the differential pressure sensors.